Additive manufacturing or rapid prototyping methods for producing objects comprise layer-by-layer solidification of a material, such as a metal powder material, using a high energy beam, such as a laser beam or electron beam. A powder layer is deposited on a powder bed in a build chamber and a laser beam is scanned across portions of the powder layer that correspond to a cross-section of the object being constructed. The laser beam melts or sinters the powder to form a solidified layer. After selective solidification of a layer, the powder bed is lowered by a thickness of the newly solidified layer and a further layer of powder is spread over the surface and solidified, as required.
During the melting or sintering process, debris (e.g. condensate, unsolidified particles of powder etc) is produced within the build chamber. It is known to introduce a gas flow through the build chamber in an attempt to remove debris from the chamber in the gas flow. For example, the M280 model of machine produced by EOS GmbH, Munich, Germany comprises a series of gas outlet nozzles located in the build chamber to the rear of the powder bed that pass a flow of gas to a series of exhaust vents that are located in the build chamber at the front of the powder bed. In this manner, a planar layer of gas flow is created at the surface of the powder bed. A similar arrangement is provided in Renishaw's AM250 and AM125 machines, wherein apertures in the build chamber either side of a powder bed provide substantially planar gas flow across the powder bed.
It is known from DE102005014483 A1 to use four laser beams to scan a powder bed, each laser beam solidifying powder in a different quadrant of the powder bed. Such an arrangement may increase build speed because different parts of an object or different objects located in different quadrants can be built simultaneously with different laser beams.
US2013/0112672 discloses an additive manufacturing assembly in which a primary energy beam is split into a plurality of secondary laser beams. The secondary beams are directed by individually movable energy directing elements into separate regions of a workspace. A transit assembly may be provided for conveying energy transmitting devices, the transit assembly comprising a first carriage movable in a first direction and a second carriage that moves on the first carriage in a second direction. Each of the energy transmitting devices emits a separate laser beam that is independently and separately movable for directing energy over separate portions of the part.